Advanced composites promise savings, increased strength and durability.
The recent successful repair of the historic Münchenstein Bridge in Switzerland is advancing Australian efforts to develop a repair system for the world’s aging metallic infrastructure, using advanced carbon fibre reinforced polymer (CFRP) materials.
In a collaboration with leading Swiss engineering research institutes, infrastructure authorities and industry, Professor Xiao-Ling Zhao, Chair of Civil Engineering at Monash University, participated in the development of the solution for the bridge. Built in 1892 across the Birs River near Basel, the bridge carries both passenger and freight trains.
Two girders, the most critical elements against fatigue on the 45.2 metre single span wrought iron bridge, were strengthened using carbon fibre reinforced polymer materials. The repair system does not required glue to bond the CFRP plates to the metal, which substantially reduces the time and cost needed for surface preparation, says Professor Masoud Motavalli from the Swiss Federal Laboratories for Materials Science and Technology (a major contributor to the Münchenstein Bridge project). The system is also able to pre-stress the CFRP plates to the desirable level to prevent fatigue cracking.
In comparison, the conventional method of repairing or strengthening aging metallic structures often involves bulky and heavy steel plates that are difficult to fix and prone to corrosion, as well as being prone to fatigue of their own. The process can also be harmful to sensitive environments, says Professor Zhao.
Urgent global need
Repairing and strengthening metallic infrastructure, especially bridges, to prolong service life and take increasing loads, is becoming an urgent need globally, says Professor Zhao. In Europe, nearly 70 per cent of metallic bridges are older than 50 years and 30 per cent are over 100 years. In the USA, more than 62,000 metallic bridges are classified as structurally deficient.
Similarly, there are major deficiencies in Australia’s state and local road bridges, according to Engineers Australia’s latest Infrastructure Report Card.
Professor Zhao says the success of the Münchenstein Bridge repair confirmed CFRP had great potential to strengthen metallic infrastructure in terms of increased strength (five to six times stronger than steel), ductility, energy absorption and fatigue life.
Recognising the need, Monash research, mainly sponsored by several Australian Research Council (ARC) Discovery Grants in collaboration with researchers in the USA, China and Switzerland, is seeking to develop a reliable CFRP strengthening system that will reduce the maintenance time and increase the service life of metallic infrastructure, even under harsh environmental conditions. Further, a CFRP repair solution would also increase the load carrying capacity of major bridges to cope with increased tonnage carried by trucks and trains, says Professor Zhao.
The Melbourne West Gate Bridge widening project also confirms the benefits of CFRP in infrastructure repair and Australia’s research capabilities in this field. Retro-fitting structures with advanced composite materials is a focus of research by Riadh Al-Mahaidi, Professor of Structural Engineering at Swinburne University of Technology and an Adjunct Professor at Monash. Professor Al-Mahaidi played a key role in the development of the CFRP strengthening solution for the widening of the West Gate Bridge. The innovative solution to strengthen the bridge’s concrete deck, developed and put to the test at Monash and then Swinburne, has gained global recognition.
It saved millions of dollars in implementation costs, according to consulting engineers for the Westgate Bridge Strengthening Alliance, Sinclair Knight Mertz (SKM).
Material-specific solutions required
However, this knowledge and expertise developed for use of CFRP in concrete repair cannot be directly applied to metallic structures due to the distinct difference between the debonding mechanism of the two materials, plus the unique failure modes for metallic members and connections.
Professors Zhao, Motavalli (an Adjunct Professor at Monash) and Al-Mahaidi are seeking to progress development of CFRP systems for infrastructure repair through a partnership with VicRoads and S&P Clever Reinforcement Company. An ARC Linkage Grant announced in June 2014 gives a boost to this research.